arm64/mm: Hoist barriers out of set_ptes_anysz() loop

arm64/mm: Hoist barriers out of set_ptes_anysz() loop

set_ptes_anysz() previously called __set_pte() for each PTE in the
range, which would conditionally issue a DSB and ISB to make the new PTE
value immediately visible to the table walker if the new PTE was valid
and for kernel space.

We can do better than this; let's hoist those barriers out of the loop
so that they are only issued once at the end of the loop. We then reduce
the cost by the number of PTEs in the range.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Tested-by: Luiz Capitulino <luizcap@redhat.com>
Link: https://lore.kernel.org/r/20250422081822.1836315-7-ryan.roberts@arm.com
Signed-off-by: Will Deacon <will@kernel.org>